The invention relates to a one-way clutch, and more particularly, to a one-way clutch in which tongue-like flaps of a spring provided on an inner diameter side of a retainer do not interfere with portions of sprags or portions of the retainer and are made greater in strength, to thereby improve engagement performance.
A one-way clutch used in an automatic transmission of an automobile is interposed between outer and inner rings, and transmission and interruption of power is effected repeatedly. As shown in FIG. 9, such a one-way clutch is usually constituted by sprags 15, a retainer 13, and a spring 14, and is placed in an annular space 20 defined between an outer ring 11 and an inner ring 12. When the one-way clutch is rotated in one direction at the time of transmission of power, by means of relative rotation between the outer ring 11 and the inner ring 12, the sprags 15 act as wedges, whereby the outer ring 11 and the inner ring 12 rotate in an integrated fashion (a locked state). When the retainer 13 is rotated in the opposite direction, the sprags 15 are released from a wedge-like state and perform idle running, thereby interrupting power transmission (an unlocked state). In some cases the retainer consists of two retainers; that is, an outer retainer and an inner retainer. The two retainers are rotated relatively under a locked state and under an unlocked state.
In such a one-way clutch of sprag type, the spring 14 is guided along an inner diameter side of the retainer 13, thereby enabling correct radial positioning of the sprags 15 retained by the spring 14. Tongue-like flaps 14 of the spring 14 usually impart pre-stress (i.e., force) to the sprags 15 toward a direction in which the sprags 15 are to be locked, thus contributing to an engagement characteristic. As mentioned, the tongue-like flaps 14t become deformed, as occasion demands, through repeated idle running and engaging actions of the sprags 15. For this reason, the tongue-like flaps that impart pre-stress to the sprags 15 are subjected to repeated stress. In many cases, each of the tongue-like flaps is provided with a rounded section for enhancing the rigidity thereof.
As indicated by chain double-dashed lines shown in FIG. 9, when a rounded section 14a of the tongue-like flap 14t of the spring is oriented outward, the rounded section 14a may interfere with the inner diameter side of the retainer 13, because the spring is usually guided toward the inner diameter side of the retainer 13. When the sprags are subjected to maximum inclination; for example, in the case that the tongue-like flaps 14t of the spring are provided respectively with the outward-oriented rounded sections 14a or that excessive decentering has arisen between the outer and inner rings, only the extremities of the tongue-like flaps 14t fail to act on the sprags, and the rounded sections 14a interfere with the sprags 15. As a result, the tongue-like flaps 14t fail to exhibit appropriate spring force, thereby deteriorating the engagement characteristic.
FIG. 10 shows the configuration of a related-art one-way clutch. As illustrated, with a view to addressing repeated stress, rounded sections 24a are formed on radially inner-diameter sides of respective tongue-like flaps 24t of a spring 24 provided along an inner diameter side of a retainer 23, to thereby enhance rigidity of the tongue-like flaps 24t. When the rounded sections 24a oriented toward an inner diameter are provided, as in the case of the tongue-like flaps 24t of the spring 24, there is apprehension that the rounded sections 24a may interfere with the adjacent sprags 25 at the time of idle running operation. Hence, large rounded sections cannot be provided.
FIG. 11 shows a one-way clutch constituted by a retainer 23 having a flange section 23f, a spring 24, and sprags 25.
In such a one-way clutch, the retainer 23 and the outer ring are rotated synchronously. Hence, in many cases, the retainer 23 is fitted into an outer ring (not shown) while being given interference allowance. To this end, an outer diameter of the retainer 23 (i.e., an outer diameter of the flange 23f) is made slightly larger than the inner diameter of a track surface of the outer ring, whereby the retainer 23 is press-fitted to the outer ring. Thus, there is provided a one-way clutch imparted fixing force. By the pressure required when the retainer 23 is press-fitted into an inner peripheral surface of the outer ring, the retainer 23 becomes eccentricity with respect to the outer ring, thereby rendering clearance between the sprags 25 and the pockets of the retainer 23 narrow. In order to avoid such a problem, there has been proposed a method of forming notches 23c in the flange 23f of the retainer 23 at uniform intervals with reference to a circumferential direction so as to divide the flange 23f into pieces of equal parts (as described in Japanese Utility Model Publication No. 43370/1994). Alternatively, a slightly-oval retainer is fixedly pressed into an outer ring such that the outer ring operates along with the retainer in an integrated fashion (Japanese Utility Model Publication No. 10233/1994).
As shown in FIG. 9, the spring 14 is provided on the internal diameter side of the retainer 13 for retaining the sprags 15. Tongue-like flaps 14t of the spring 14 force the sprags 15, at all times, toward a direction in which the sprags 15 are to be locked. Since the retainer 13 is to be operated in synchronism with the outer ring 11, when the retainer 13 of slightly ellipse shape is press-fitted into the inner peripheral surface (i.e., track surface) of the outer ring 11, the spring 14 becomes locally deformed toward the radial center because of, particularly, reaction force stemming from press-fitting of the ellipse portion of the retainer 13. Therefore, the force exerted on the sprags 15 by the tongue-like flaps 14t of the spring 14 which imparts pre-stress to the sprags 15 is weakened by the local deformation of the spring 14. In areas where the spring 14 is deformed to a great extent, the attitude of the sprags 15 is inclined heavily toward the direction of idle running. When the sprags 15 move from an idle running position to an engagement position, the amount of deformation of the tongue-like flaps 14t of the spring 14 becomes greater, thereby rendering the tongue-like flaps 14t easy to break. Such breakage in turn induces an engagement failure in a one-way clutch.